The present invention relates generally to a method of measuring the concentration of at least one reactant, product or byproduct of liquid-phase oxidation processes for making N-(phosphonomethyl)glycine (also known in the agricultural chemical industry as xe2x80x9cglyphosatexe2x80x9d) and related compounds and a method for controlling the oxidation process based on the concentration measured. More particularly, this invention relates to a method for quantitatively analyzing aqueous mixtures comprising an N-(phosphonomethyl)iminodiacetic acid (xe2x80x9cNPMIDAxe2x80x9d) substrate (i.e., N-(phosphonomethyl)iminodiacetic acid, a salt of N-(phosphonomethyl)iminodiacetic acid, or an ester of N-(phosphonomethyl)iminodiacetic acid), an N-(phosphonomethyl)glycine product (i.e., N-(phosphonomethyl)glycine, a salt of N-(phosphonomethyl)glycine, or an ester of N-(phosphonomethyl)glycine), formaldehyde, formic acid, N-methyl-N-(phosphonomethyl)glycine (xe2x80x9cNMGxe2x80x9d), aminomethylphosphonic acid (AMPA), N-methyl-aminomethylphosphonic acid (MAMPA) or aminomethylphosphonic acid (xe2x80x9cAMPAxe2x80x9d)) using infrared spectroscopy and more particularly Fourier transform infrared (FTIR) spectroscopy. The present invention also relates to a method for using the analytical method to control a liquid process wherein an N-(phosphonomethyl)iminodiacetic acid substrate is oxidized to form a N-(phosphonomethyl)glycine product.
N-(phosphonomethyl)glycine is described by Franz in U.S. Pat. No. 3,799,758. N-(phosphonomethyl)glycine and its salts are conveniently applied as a post-emergent herbicide in an aqueous formulation. It is a highly effective and commercially important broad-spectrum herbicide useful in killing or controlling the growth of a wide variety of plants, including germinating seeds, emerging seedlings, maturing and established woody and herbaceous vegetation, and aquatic plants.
One of the more widely accepted methods of making N-(phosphonomethyl)glycine compounds comprises oxidatively cleaving a carboxymethyl substituent from a N-(phosphonomethyl)iminodiacetic acid substrate. Over the years, a wide variety of methods have been disclosed for conducting this oxidation. See generally, Franz, et al., Glyphosate: A Unique Global Herbicide (ACS Monograph 189, 1997) at pp. 233-62 (and references cited therein); Franz (U.S. Pat. No. 3,950,402); Hershman (U.S. Pat. No. 3,969,398); Chou (U.S. Pat. No. 4,624,937); Chou (U.S. Pat. No. 4,696,772); Ramon et al. (U.S. Pat. No. 5,179,228); Felthouse (U.S. Pat. No. 4,582,650); Siebenhaar et al. (PCT/EP99/04587); and Ebner et al. (PCT/US99/03402). Generally, these processes produce suitable yields, however they also produce formaldehyde (HCHO) as a byproduct. Formic acid (HCO2H) also tends to be formed by the oxidation of the formaldehyde byproduct. These byproducts are undesirable because they tend to react with the N-(phosphonomethyl)glycine product to produce unwanted by-products (mainly N-methyl-N-(phosphonomethyl)glycine (xe2x80x9cNMGxe2x80x9d) and N-formyl-N(phosphonomethyl)glycine (xe2x80x9cNFGxe2x80x9d)) which reduce the N-(phosphonomethyl)glycine product yield. In addition, the formaldehyde by-product itself is undesirable because of its potential toxicity.
The oxidation reaction may be practiced using a wide range of temperatures, and at pressures ranging from sub-atmospheric to super-atmospheric. Moreover, the precise conditions and reaction rate under which the oxidation process is conducted affects the concentration of not only the un-reacted N-(phosphonomethyl)iminodiacetic acid substrate and the N-(phosphonomethyl)glycine in the final reaction mixture, but also the concentrations of undesirable byproducts (e.g., formaldehyde, formic acid, N-methyl-N-(phosphonomethyl)glycine (xe2x80x9cNMGxe2x80x9d), and aminomethylphosphonic acid (xe2x80x9cAMPAxe2x80x9d)). Although the analysis of these mixtures may be performed by periodically sampling the reaction mixture and analyzing the sample using high pressure liquid chromatography, a need exists for an analytical method which allows for on-line analysis to provide real-time concentration data to allow for real-time monitoring and control of the oxidation process.
Among the objects of the present invention, therefore is the provision of an analytical method for determining the concentration of an analyte of an aqueous mixture comprising N-(phosphonomethyl)iminodiacetic acid, a salt of N-(phosphonomethyl)iminodiacetic acid, an ester of N-(phosphonomethyl)iminodiacetic acid), N-(phosphonomethyl)glycine, a salt of N-(phosphonomethyl)glycine, an ester of N-(phosphonomethyl)glycine), formaldehyde, formic acid, N-methyl-N-(phosphonomethyl)glycine, N-methyl-aminomethylphosphonic acid, aminomethylphosphonic acid, or mixtures thereof; the provision of an analytical method for determining the concentration of an analyte in said aqueous mixture to provide real time or substantially real time measurements of a process for oxidizing an N-(phosphonomethyl)iminodiacetic acid substrate to form a N-(phosphonomethyl)glycine product; and the provision of a process for oxidizing an N-(phosphonomethyl)iminodiacetic acid substrate to form a N-(phosphonomethyl)glycine product wherein as part of the process, measuring the concentration of an analytic using the analytical method of the present invention, and controlling the oxidation process in response to the measurement.
Briefly therefore, the present invention is directed to a method for determining the concentration of an analyte of an aqueous mixture comprising N-(phosphonomethyl)iminodiacetic acid, a salt of N-(phosphonomethyl)iminodiacetic acid, an ester of N-(phosphonomethyl)iminodiacetic acid), N-(phosphonomethyl)glycine, a salt of N-(phosphonomethyl)glycine, an ester of N-(phosphonomethyl)glycine), formaldehyde, formic acid, N-methyl-N-(phosphonomethyl)glycine, N-methyl-aminomethylphosphonic acid, aminomethylphosphonic acid, or mixtures thereof. The method includes measuring an electromagnetic absorbance spectrum for the aqueous mixture over an infrared wavenumber range of from about 200 cmxe2x88x921 to about 5000 cmxe2x88x921 and using data from the electromagnetic absorbance spectrum in a chemometric model to determine the concentration of the analyte in the aqueous mixture, the chemometric model being a mathematical relationship between the concentration of the analyte in the aqueous mixture as a function of the electromaganetic absorbance spectrum of the mixture.
The present invention is further directed to a process for the preparation of an N-(phosphonomethyl)glycine product selected from the group consisting of N-(phosphonomethyl)glycine, a salt thereof or an ester thereof by oxidation of an N-(phosphonomethyl)iminodiacetic acid substrate selected from the group consisting of N-(phosphonomethyl)iminodiacetic acid, a salt thereof or an ester thereof. The process includes contacting said substrate with an oxygen containing gas in the presence of a catalyst for the reaction, measuring the concentration in real time or substantially real time of an analyte in the reaction mixture, the analyte being selected from a group consisting of N-(phosphonomethyl)iminodiacetic acid, a salt of N-(phosphonomethyl)iminodiacetic acid, an ester of N-(phosphonomethyl)iminodiacetic acid), N-(phosphonomethyl)glycine, a salt of N-(phosphonomethyl)glycine, an ester of N-(phosphonomethyl)glycine), formaldehyde, formic acid, N-methyl-N-(phosphonomethyl)glycine, N-methyl-aminomethylphosphonic acid, or aminomethylphosphonic acid and controlling the conversion of N-(phosphonomethyl)iminodiacetic acid substrate to affect the concentration of the measured analyte in the reaction mixture.
Other objects and features of this invention will be in part apparent and in part pointed out hereinafter.